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NCERT Class XI Mathematics - Conic Sections - Solutions

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Question : 50 of 71
Marks: +1, -0
9y24x29y^2 - 4x^2 = 36
Solution:  
Given equation of hyperbola is 9y24x29y^2 - 4x^2 = 36
i.e., 9y2364x236\frac{9y^2}{36} - \frac{4x^2}{36} = 1 ⇒ y24x29\frac{y^2}{4} - \frac{x^2}{9} = 1 , which is of the form y2a2x2b2\frac{y^2}{a^2} - \frac{x^2}{b^2} = 1.
The foci and vertices of the hyperbola lie on y-axis.
Now, a2a^2 = 4 ⇒ a = 2 and b2b^2 = 9 ⇒ b = 3
Also, c2c^2 = a2+b2a^2 + b^2 = 4 + 9 = 13 ⇒ c = 13\sqrt{13}
∴ Coordinates of foci are (0, ± c) i.e. (0, ± 13\sqrt{13})
∴ Coordinates of vertices are (0, ±a) i.e. (0, ±2)
Eccentricity (e) = ca\frac{c}{a} = 132\frac{\sqrt{13}}{2}
Length of latus rectum = 2b2a\frac{2b^2}{a} = 2×92\frac{2 \times 9}{2} = 9.
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